The present invention relates to a honeycomb filter used to capture and eliminate particulate matter or the like from exhaust gases.
In recent years, environmental considerations have increased the necessity for eliminating particulate matter contained in exhaust gases of combustion apparatuses, such as an internal combustion engine and a boiler. In particular, regulations relating to elimination of particulate matter (PM) including graphite particles or the like discharged from diesel engines tend towards tightening in Europe, the United States, and Japan. A honeycomb structured body referred to as a diesel particulate filter (DPF) has been used to capture and eliminate substances such as PM. A honeycomb structured body is accommodated in a casing that is arranged on an exhaust passage for a combustion apparatus. The honeycomb structured body has a large number of cells that extend in the longitudinal direction of the structure. The cells are partitioned by partitions. In every pair of adjacent cells, one cell has an open end on one side and the other cell has an open end on the opposite side. The opens cells are sealed by a plug. Plugs are arranged in a lattice on each end surface (inlet side end surface and outlet side end surface) of the honeycomb structured body. Exhaust gas enters open cells at the inlet side end surface of the honeycomb structured body, flows through the porous partitions, and is discharged from adjacent open cells at the outlet side end surface. For example, PM discharged from a diesel engine is captured by the partitions that function as a filter, and accumulates on the partitions. The PM accumulating on the partitions is burned and eliminated by a heating means, such as a burner or a heater, or by heat from the exhaust gas.
JP-A 1-258715 describes a conventional honeycomb filter integrally including a honeycomb structured body and plugs for sealing selected opened ends of cells of the honeycomb structured body. The honeycomb structured body is formed of a sintered porous silicon carbide containing aluminum (Al), boron (B), and iron (Fe) content of 1 wt % or less in total and containing free carbon content of 5 wt % or less. The plugs are formed of a sintered porous silicon carbide having a total content of Al, B, and Fe content that is less than the same total of the honeycomb structured body and having a free carbon content of 5 wt % or less. The entire contents of JP-A 1-258715 are incorporated herein by reference.
A honeycomb filter of the present invention includes at least one pillar-shape honeycomb structured body including a plurality of cells partitioned by partitions, and plugs for sealing upstream openings of a plurality of first cells selected from the plurality of cells and for sealing downstream openings of a plurality of second cells selected from the plurality of cells, and is characterized in that each of the plugs is formed of a material having a greater total content of aluminum, iron, boron, silicon, and free carbon than a material forming the honeycomb structured body.
In the honeycomb filter of the present invention, it is preferred that each of the plugs has a first end surface adjacent to an opening of the corresponding one of the cells and a second end surface opposite the first end surface, and that the second end surface is formed so that a length from the first end surface to the second end surface is not constant in a direction perpendicular to a center axis of the cell.
In the honeycomb filter of the present invention, it is preferred that each of the plugs has a first end surface adjacent to an opening of the corresponding one of the cells and a second end surface opposite the first end surface, and the second end surface includes a recess in a central position corresponding to a center axis of the cell.
In the honeycomb filter of the present invention, it is preferred that each of the plugs has an end surface including a recess and comes in contact with the partition outward from the recess at a contact angle of about 1 to about 50 degrees.
In the honeycomb filter of the present invention, it is preferred that the contact angle is about 1 to about 45 degrees.
In the honeycomb filter of the present invention, it is preferred that the contact angle is about 1 to about 30 degrees.
In the honeycomb filter of the present invention, it is preferred that each of the plugs has a first end surface adjacent to an opening of the corresponding one of the cells and a second end surface opposite the first end surface, and that the second end surface includes a projection at a central position corresponding to a center axis of the cell.
In the honeycomb filter of the present invention, it is preferred that each of the plugs has an end surface including a projection and comes in contact with the partition outward from the projection at a contact angle of about 91 to about 179 degrees.
In the honeycomb filter of the present invention, it is preferred that the contact angle is about 91 to about 135 degrees.
In the honeycomb filter of the present invention, it is preferred that each of the plugs have a length varies depending on the distance from the center axis of the corresponding cell in a direction orthogonal to the center axis of the corresponding cell and that the difference between a maximum value and a minimum value of the length of each cell is about fifteen times or less the thickness of the partition.
In the honeycomb filter of the present invention, it is preferred that the difference between a maximum value and a minimum value of the length of each cell is about ten times or less the thickness of the partition.
In the honeycomb filter of the present invention, it is preferred that the honeycomb structured body comprises at least one material selected from the group consisting of cordierite, zirconium phosphate, aluminum titanate, silicon carbide, and a silicon metal-silicon carbide composite.
In the honeycomb filter of the present invention, it is preferred that at least part of the partition carries a catalyst.
In the honeycomb filter of the present invention, it is preferred that the honeycomb structured body is formed by bonding a plurality of honeycomb members with a bonding material, with each honeycomb member having an outer wall, partitions arranged inward from the outer wall, and a plurality of cells partitioned by the partitions and functioning as flow passages for fluid.
In the honeycomb filter of the present invention, it is preferred that a coating layer is applied on an outer circumference of the honeycomb structured body.
In the honeycomb filter of the present invention, it is preferred that the total content of Al, Fe, B, Si, and free carbon in the material for forming the plugs is more than about 0.35 mass %.
In the honeycomb filter of the present invention, it is preferred that the total content of Al, Fe, B, Si, and free carbon in the material for forming the plugs is about 1.5 mass % or less.
In the honeycomb filter of the present invention, it is preferred that the at least one pillar-shape honeycomb structured body is a single monolithic-type honeycomb structure body without a bonding layer.
In the honeycomb filter of the present invention, it is preferred that the monolithic-type honeycomb structure body comprises cordierite, zirconium phosphate, or aluminum titanate.
The present invention proposes a manufacturing method for honeycomb filter including at least one pillar-shape honeycomb structured body including a plurality of cells partitioned by partitions, and plugs for sealing upstream openings of a plurality of first cells selected from the plurality of cells and for sealing downstream openings of a plurality of second cells selected from the plurality of cells. The method is characterized by forming the at least one pillar-shape honeycomb structured body from a material having aluminum, iron, boron, silicon, and free carbon with a desired content, and forming the plugs from a material having a greater total content of aluminum, iron, boron, silicon, and free carbon than the material forming the at least one pillar-shape honeycomb structured body.
In the manufacturing method of the present invention, it is preferred that each of the plugs has a first end surface adjacent to an opening of the corresponding one of the cells and a second end surface opposite the first end surface, and the step of forming the plugs includes forming the second end surface so that a length from the first end surface to the second end surface is not constant in a direction perpendicular to a center axis of the cell.
In the manufacturing method of the present invention, it is preferred that each of the plugs has a first end surface adjacent to an opening of the corresponding one of the cells and a second end surface opposite the first end surface, and the step of forming the plugs includes forming a recess at a central position of the second end surface corresponding to a center axis of the cell.
In the manufacturing method of the present invention, it is preferred that the step of forming the plugs includes forming each of the plugs so that each of the plugs has an end surface including a recess and comes in contact with the partition outward from the recess at a contact angle of about 1 to about 50 degrees.
In the manufacturing method of the present invention, it is preferred that the contact angle is about 1 to about 45 degrees.
In the manufacturing method of the present invention, it is preferred that the contact angle is about 1 to about 30 degrees.
In the manufacturing method of the present invention, it is preferred that the step of forming the plugs includes forming each of the plugs so that each of the plugs has a first end surface adjacent to an opening of the corresponding one of the cells and a second end surface opposite the first end surface, and the second end surface includes a projection at a central position corresponding to a center axis of the cell.
In the manufacturing method of the present invention, it is preferred that the step of forming the plugs includes forming each of the plugs so that each of the plugs has an end surface including a projection and comes in contact with the partition outward from the projection at a contact angle of about 91 to about 179 degrees.
In the manufacturing method of the present invention, it is preferred that the contact angle is about 91 to about 135 degrees.
In the manufacturing method of the present invention, it is preferred that each of the plugs have a length varies depending on the distance from the center axis of the corresponding cell in a direction orthogonal to the center axis of the corresponding cell, and the difference between a maximum value and a minimum value of the length of each cell is about fifteen times or less the thickness of the partition.
In the manufacturing method of the present invention, it is preferred that the difference between a maximum value and a minimum value of the length of each cell is about ten times or less the thickness of the partition.
In the manufacturing method of the present invention, it is preferred that the material forming the honeycomb structured body comprises at least one material selected from the group consisting of cordierite, zirconium phosphate, aluminum titanate, silicon carbide, and a silicon metal-silicon carbide composite.
In the manufacturing method of the present invention, it is preferred to further include providing a catalyst on at least part of the partition.
In the manufacturing method of the present invention, it is preferred that the step of forming the at least one pillar-shape honeycomb structured body includes bonding a plurality of honeycomb members with a bonding material, with each honeycomb member having an outer wall, partitions arranged inward from the outer wall, and a plurality of cells partitioned by the partitions and functioning as flow passages for fluid.
In the manufacturing method of the present invention, it is preferred to further include applying a coating layer on an outer circumference of the honeycomb structured body.
In the manufacturing method of the present invention, it is preferred that the total content of Al, Fe, B, Si, and free carbon in the material for forming the plugs is more than about 0.35 mass %.
In the manufacturing method of the present invention, it is preferred that the total content of Al, Fe, B, Si, and free carbon in the material for forming the plugs is about 1.5 mass % or less.
In the manufacturing method of the present invention, it is preferred that the at least one pillar-shape honeycomb structured body is a single monolithic-type honeycomb structure body without a bonding layer.
In the manufacturing method of the present invention, it is preferred that the monolithic-type honeycomb structure body comprises cordierite, zirconium phosphate, or aluminum titanate.
In the manufacturing method of the present invention, it is preferred that the step of forming the at least one pillar-shape honeycomb structured body includes adding a shortfall of impurities to the material for forming the at least one pillar-shape honeycomb structured body if the content of aluminum, iron, boron, silicon, and free carbon in that material is less than the desired content.